I know that emanation from material such as rooks to the air space or pores between them and exhalation from this pores to air indoor or outdoor. But as example in Ra-226 source? Emanation? Why?
is the main different depend on the mechanism of radon moving? diffusion or convection or pressure gradient ?
Some authors use emanation and exhalation interchangeably. The correct use is shown in your diagram. Radon in the pores is exhaled by diffusion if there is no movement (convection) of the gas in the pores. Radon is removed by convection if there is movement in the pores, gaps, and cracks in the material. Convection can be caused by temperature differences in the material, water intrusion, or pressure difference caused by movement of air across the surface of the substance or atmospheric pressure changes. Pressure differential in a structure can be caused by air movement (advection) or temperature differentials.
prof/Joseph L Alvarez . many thanks, yes i understand this idea but confused from difrent papers with diffrent uses of emanation and exhalation
Emanation is the movement of the radon atom inside the grain and toward the intergranular space. After radon is generated from radium in the solid grains, they emanate the radon atom toward pore gases or fluids in the intergranular space and then radon can migrate at significant distances from the site of generation. Then it enter the atmosphere before undergoing radioactive decay in the exhalation process. The emanation coefficient (the fraction of radon atoms that escape from a mineral grain into the pore space) is the most important parameter which characterizes the behavior of radon in soil and rock materials.
Exhalation is the movement of radon atom within the intergranular space as a gas phase dissolved in groundwater in the saturated zone or as gas mixed to soil pore air in the unsaturated zone. Due to the diffusion and convection the radon can be exhaled from the pore space into the air. The radon exhalation greatly depends on the features of the investigated material, such as the thickness, the internal structure and the moisture content of the solid phase as well.
Please, you can refer for example to
Hassan et al 2009 Radon Migration Process and Its Influence Factors; Review. Jpn. J. Health Phys., 44 (2), 218 ～ 231 (2009)
Emanation: Property that points to the potentiality of "exit" for a radon atom.
Exhalation: Property that points to the "exit" of radon from a grain-type material (rock, soil building material).
Crystalisation of a grain may block radon exit. If so, radon progeny are also blocked inside the grain.
Upon exit, radon atoms migrate near or far depending mainly on the type of soil & rock and the migration mechanism (advection, convection, earthquake etc.) The migration yields finally to certain amount of radon that "flow" out of soil or rock. This is characterised in general as emanation. It is the emanated radon that travels-migrates.
certain amounts, dilute in atmosphere (strictly emanate) and the remaining are diluted in water or remain in soils pores. Earthquake driven events may yield to unexpectedly radon disturbances.
I agree with all above mentioned answers, besides the "term emanation coefficient" is defined as the fraction of radon atoms (%) which escape the solid phase in which they are formed and become free to diffuse through the bulk medium. Or it is the process of radon liberation from the solid particle in which it is originated. While the term "Exhalation rate" is referred to the processes of releasing radon gas to the atmosphere.
Radon exhalation is the amount of radon (radon activity) as obtained from a given layer (geological material on the surface/surface exposure) mainly the outer thinner part of the crust. In the deeper material(within a geological strata), due to the attenuation of alpha particles from the uranium rich rock and/or thorium (another isotope of radium) it decreases. It is primarily due to diffusion, advection and convection as modes of radon transport. The presence of fractures, shearing, deformations, tectonic lineaments and faulting aids in the upward migration of radon. On the other hand Radon emanation is dependent on permeability of the rock, other lithological properties like rock alteration, erosion, diagenetic changes, to name a few. It also dependents on the nature of uranium and/or thorium. The moisture content of the specific lithology could affect both exhalation and emanation however the latter is affected more predominantly. In general, Exhalation is a source function while Emanation is more dependent on the nature of the media like rock type, nature of radioactive minerals, permeability to name a few. The latter also gets altered due to the differences in the geochemical behaviour of uranium and thorium (in specific lithology) and the inherent heterogeinity in rocks and minerals as both uranium and thorium behave somewhat ike trace elements except in radioactive mineralized regions and should also depend on Th/U ratios in specific lithology.
emanation-escape of radon atom from decay chain in the rock to the pore sites.
exhalation- escape of radon atom from pores to the atmosphere.
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